Some types of implantable medical devices (IMDs) provide therapeutic electrical stimulation to and/or monitor activity of a tissue of a patient via electrodes of one or more implantable leads that include electrodes. Examples of such devices include implantable cardiac pacemakers, cardioverters, defibrillators, neurostimulators, muscle stimulators, or the like. In the case of therapeutic electrical stimulation, the electrical stimulation may be delivered to the tissue via the electrodes of implantable leads in the form of neurostimulation pulses, pacing pulses, cardioversion shocks, defibrillation shocks, cardiac resynchronization or other signals. In some cases, electrodes carried by the implantable leads may be used to sense one or more physiological signals to monitor the condition of a patient and/or to control delivery of therapeutic electrical stimulation based on the sensed signals.
An IMD may be exposed to a disruptive energy field for any of a number of reasons. For example, one or more medical procedures may need to be performed on the patient within whom the IMD is implanted for purposes of diagnostics or therapy. For example, the patient may need to have a magnetic resonance imaging (MRI) scan, computed tomography (CT) scan, electrocautery, diathermy or other medical procedure that produces a magnetic field, electromagnetic field, electric field or other disruptive energy field.
The disruptive energy field may induce energy on one or more of the implantable leads coupled to the IMD, which could alter the operation of the IMD. For example, the induced energy may produce lead heating, radio frequency (RF) rectification, and/or device heating effects, which could alter the pacing and/or sensing thresholds within the IMD.